The present invention relates generally to a scanner device for use in a facsimile machine or the like. The scanner device reads a document containing text, graphics, photograph, etc.
When a document is read out with a scanner device or a reading device, it is sometimes difficult to read a fine line extending in a main scanning direction (hereinafter referred to as "horizontal fine line"). Such a difficulty occurs because the horizontal fine line may not be perceived by the scanner device. When the level of the picked up image raises above and falls below a threshold as the document is scanned, the line will be reproduced in undulated fashion rather than straightly extending in the horizontal direction. It has been a common practice to reproduce the horizontal fine line in a fine resolution mode in which the number of scanning lines per a unit length in the auxiliary scanning direction is increased when the document is scanned.
The fine resolution mode is, however, disadvantageous in that it takes a long time in reading the document and it is inconvenient when a large amount of data is transmitted due to slowness of the scanning speed. If it is intended to read the horizontal fine line at a normal resolution mode in which the document is read at a normal speed with increased sensitivity, the resolution is further degraded and some of the details are lost in the reproduced image.